So far, a light-emitting device obtained by mounting an LED on a wiring board features a very high light-emitting efficiency, emits light producing heat in amounts smaller than that of incandescent lamps, and has been used for a variety of applications. However, the light-emitting device of this kind emits light in amounts smaller than those of incandescent bulbs and fluorescent lamps, and is used not for illumination purposes but as a source of light of an indicator consuming a current which is as very small as about 30 mA. The light-emitting device of this kind consumes a small electric power generating a small amount of heat, and has, hence, been realized chiefly in a structure of a so-called bullet type by burying the light-emitting element (LED) in a plastic insulating substrate (see patent document 1).
Accompanying the development of a light-emitting element featuring a high brightness and white light in recent years, further, the light-emitting device has been much used as a back light for cell phones and large liquid crystal TVs. However, an increase in the brightness of the light-emitting element is accompanied by an increase in the heat generated by the light-emitting device. To prevent a decrease in the brightness of the light-emitting element, therefore, it is becoming necessary to provide a wiring board for light-emitting element capable of quickly and highly radiating the heat produced by the light-emitting element (see patent documents 2 and 3).
Patent document 1: JP-A-2002-124790
Patent document 2: JP-A-11-112025
Patent document 3: JP-A-2003-347600